allowed transition

Allowed transitions are those that have high probability of occurring, as in the case of short-lived radioactive decay of atomic nuclei. In three-millionths of a second, for instance, half of any sample of unstable polonium-212 becomes stable lead-208 by ejecting alpha particles (helium-4 nuclei) from…

As an illustration of allowed transition in Figure 1, the only electronic transitions permitted are those in which the change in vibrational quantum number accompanying a change in electronic excitation is plus or minus one or zero, except that a 0 ↔ 0 (zero-to-zero) change is not permitted. All…

…transitions are classified as either allowed or forbidden, depending on the probability of their occurrence. In some instances, as, for example, when both the initial and final states have a total angular momentum equal to zero, there can be no single photon transition between states of any kind. The allowed…

Selection rules, accordingly, may specify “allowed transitions,” those that have a high probability of occurring, or “forbidden transitions,” those that have minimal or no probability of occurring. Selection rules usually are stated as sets of changes in one or more quantum numbers that characterize properties changed by the transition in…